Recently, with the development of technologies, liquefied gas, such as liquefied natural gas and liquefied petroleum gas, has been widely used, instead of gasoline or diesel.
Liquefied natural gas is gas obtained by cooling and liquefying methane obtained by refining natural gas collected from a gas field, and is colorless and transparent liquid, and produces few pollutants and has a high calorific value, so that the liquefied natural gas is a very excellent fuel. On the other hand, the liquefied petroleum gas is a fuel obtained by compressing and liquefying gas, of which main components are propane (C3H8) and butane (C4H10), collected from an oilfield, together with petroleum at room temperature. The liquefied petroleum gas is colorless and odorless, similar to liquefied natural gas, and has been widely used as fuel for home, a business, an industry, and a vehicle.
The liquefied gas is stored in a liquefied gas storing tank installed on a ground, or a liquefied gas storing tank included in a vessel, which is a transportation means sailing the ocean, and a volume of the liquefied natural gas is decreased by 1/600 by liquefaction, and a volume of propane is decreased by 1/260 and a volume of butane is decreased by 1/230 by liquefaction in liquefied petroleum gas, so that storage efficiency is high.
The liquefied gas is supplied to and used in various sources of demand, and an LNG fuel supply method of driving an engine by using LNG as fuel in an LNG carrying vessel carrying liquefied natural gas has been recently developed, and the method of using LNG as the fuel of the engine has been applied to other vessels, in addition to the LNG carrying carrier.
However, a temperature, a pressure, and the like of liquefied gas demanded by a source of demand, such as an engine, may be different from a state of liquefied gas stored in a liquefied storing tank. Accordingly, in recent days, technology of supplying LNG to a source of demand by controlling a temperature, a pressure, and the like of the liquefied gas stored in a liquid state has been continuously researched and developed.